1. Field of the Invention
This invention relates to lens mountings having movable lens cells, and more particularly to the structure of a device for movably fitting the lens cell into a fixed support tube.
2. Description of the Prior Art
In the past, among several kinds of lens mountings there has been one which is adapted to be used with an optical system that is constructed with lens members movable relative to other lens members to effect, for example, focusing, zooming, or the like. And, a cell holding the movable lens member is slidably mounted to a fixed support tube having, for example, three axially elongated key grooves formed in the inner surface thereof as respective keys fixed to the lens cell engage in the key grooves so as to suspend the lens cell.
FIGS. 1(a) and 1(b) in sectional views illustrate this conventional kind of lens mounting where an outer barrel 1 has three key grooves 1a, 1b and 1c formed in the inner surface thereof in spaced relation to each other by angles .theta..sub.1 and .theta..sub.2 as measured from the first key groove 1a. Assuming that a lens cell 2 has keys 3a, 3b and 3c formed on the outer surface thereof in spaced relation by angles .theta..sub.1 ' and .theta..sub.2 ' respectively, then in order to provide assurance that the lens cells 2 can be built into the outer barrel 1, it is rigorously required that .theta..sub.1 =.theta..sub.1 ' and .theta..sub.2 =.theta..sub.2 '.
On this account, it has been the general actual practice in the prior art that any two of the aforesaid three keys 3a, 3b and 3c are made movable relative to the cell body for later adjustment in position and that after that adjustment has been completed, the movable keys are then fixedly secured to the cell body by fastener screws or the like (not shown).
However, such adjusting operation is carried out manually, and as the once-established adjustment is often broken during the fixedly securing operation, it cannot be always assured that the lens cell will be readily moved in the outer barrel. Thus, the assembling operation is time-consuming and also necessitates experience and skill. Because of this, quality is not stable in uniformity from article to article, and there occurs an increase in the production cost.